University of LiègeFaculty of Applied SciencesThermodynamics Laboratory

Workshop “Commissioning and Auditing of Buildings and HVAC Systems”

Use of a Global Building-HVAC System Model for Audit

Stéphane BERTAGNOLIO

Brussels, January 28, 2008

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Content

• Introduction• Contribution to audit• Modelling• Example of use• Conclusion

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Content

• Introduction• Contribution to audit• Modelling• Example of use• Conclusion

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Introduction

• Starting audit : experimental identification of building heating, cooling and electricity consumptions almost impossible

• For auditor : difficult to differentiate chiller, pumps, fans, lighting and appliances consumptions

Calculation Method to characterize the audited system

• Important number of parameters Rational to use simulation tools rather than global

weather indexes

• Global Building-HVAC system model implemented on EES (Klein, F-Chart Software)

• Work began in the frame of “AUDITAC” and is continued in the frame of “HARMONAC – WP7”

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Content

• Introduction• Contribution to audit• Modelling• Example of use• Conclusion

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Contribution to audit

• Audit global data What is Good, Bad or Average performance ?• Useful to have benchmarks used as reference to analyse current

performances of the audited building• Comparison with current consumptions to identify main energy

consumers, energy waste and energy saving potentials• Realistic considerations :

• Building behaviour• Weather and occupancy loads• Comfort requirements• Full HVAC system

• Simulation tool adapted to the needs of auditor limited number of parameters (envelope, type of HVAC system, …)

• General tool, not adapted to highlight very specific retrofit opportunities BUT including a large range of HVAC systems

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Content

• Introduction• Contribution to audit• Modelling• Example of use• Conclusion

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Modelling overview• Two main parts : Dynamic Building model and Static HVAC system

model

• Audit Simplified Model : unique zone with a global HVAC system• Compromise between number of influences and simplicity main phenomena:

• Envelope and structure dynamic behaviour• Internal generated gains• Solar gains• Infrared losses• Ventilation and Heating/Cooling devices

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Building Model• Mono-zone model based on R-C network

• R-C “two-port” network parameters adjusted trough frequency characteristic analysis

• Simplified model default values are proposed and only general data are asked (U-values, type of thermal mass, …)

• Calculation of indoor conditions : Temperature, Humidity, CO2 contamination and comfort indexes PMV/PPD

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

HVAC system model• Classical components of AHU and TU

• TU : Heating and/or Cooling fan or induction terminal units

• AHU : AHU components models : recovery system, coils, fans, …

• Many values are proposed by default (components effectivenesses and pressure drops) or automatically computed (sizing powers)

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Control and Plant• Simple Proportional control laws

• chiller and boiler models based on correlations established using physical reference models

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Outputs, Inputs & Parameters• Main outputs

• Indoor conditions

• Global power and energy consumptions

• HVAC components specific demands

• Performances of equipments : COP, efficiencies

• Main Inputs• Weather (hourly values)

• Nominal occupancy loads and occupancy rates

• Comfort requirements

• Control laws

• Main parameters• Dimensions, orientation and characteristics

of the building envelope

• HVAC system components actually installed

• Sizing factors of main HVAC components

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Content

• Introduction• Contribution to audit• Modelling• Example of use• Conclusion

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Example of use• Typical office building

• Floor area 15000 m²• 10 floors• N/S oriented• Two 50% glazed facades• Two opaque facades• 1000 occupants• Medium thermal mass

• HVAC System• CAV• Electrical steam hum.• H/C Fan coils terminal units

• Improvements• Improved HVAC system• Improved building envelope

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Simulation results• Original Installation Theoritical consumptions ?

• Heat : 600 MWh ~ 80000 m³ • Cool : 520 MWh ~ 160 Mwhe (8%)• Elec : 1970 MWhe• Auxiliaries : 23%• Elec Steam Hum : 15%• Appl and Lighting : 53 %

• Improved HVAC System Results ?• Recovery Heat : 300 MWh and Elec : 2025 MWhe• Adiabatic Hum Heat : 600 MWh and Elec : 1700 Mwhe

• Improved building envelope Results ?• Heat : 470 MWh ~ 64000 m³ • Cool : 620 MWh ~ 190 Mwhe (10%)• Elec : 2035MWhe

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Simulation results

• Temperature profiles

• Heating / Cooling Demands

• Electrical Power Demands

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Content

• Introduction• Contribution to audit• Modelling• Example of use• Conclusion

January 28, 2008Commissioning and Auditing of Buildings and HVAC Systems

UNIVERSITY OF LIEGEFaculty of Applied Sciences

Conclusion• Simulation tool

• Dynamic R-C building model• Static HVAC system model composed of simplified HVAC components

models• Fully transparent and implemented on EES

• Helpful for the auditor :• To allow comparison between current performances and benchmarks• To differentiate and evaluates the different consumers (chiller, fans, pumps,

lighting, appliances,…)• To identify over-consumptions, energy waste and energy saving potentials • Limited quantity of parameters and use of automatically computed or default

values

• Future• Additional HVAC components : heating floor, cooling ceiling, …• Additional physical phenomena : hygroscopy ? • To reduce the number of default values by means of additional sizing

calculations…